Cases of childhood autism are up sharply, and there’s reason to wonder whether the number of cases is much higher than we suspect.

The Centers for Disease Control and Prevention reported in March that autism cases in the United States had increased 78 percent since 2002. That’s 1 in 88 U.S. children (1 in 54 boys and one in 252 girls), or about 1.1 percent of children.

A few weeks later, in May, a new study from South Korea reported that 2.3 percent of children there have autism. That’s twice the prevalence that the CDC has reported in the United States. Why such a difference?

The Korean study, lead by Yale and George Washington universities, counted cases differently. Researchers rigorously assessed individual children ages 7 to 12 in a community of 488,000 to identify known cases. In contrast, the CDC relied upon records of existing cases kept by health care and special education agencies.

Regardless of measuring methodologies, autism spectrum disorder now affects more children than diabetes, AIDS, cancer, cerebral palsy, cystic fibrosis, muscular dystrophy or Down syndrome – combined.

Why is autism on the rise? Better diagnosis alone can’t account for it.

The most cogent scientific explanation is also my greatest concern: chemical exposures. Chemically susceptible mothers who do not know they are susceptible and who therefore do not avoid exposures are at particular risk. They are more likely to have babies who share their susceptibility genes, and be raised in homes and environments in which exposures are relatively high compared to earlier generations. It’s a case where genetics loads the gun and the environment pulls the trigger.

Women who know they are chemically intolerant will work hard to help their families avoid things like pesticides, solvents, combustion products and other exposures that could lead to neurodevelopmental difficulties. This is because they are personally more aware of the adverse effects of these exposures. They will want to protect their children. However, women who are highly “masked” are less likely to avoid exposures. Although they may have multiple intolerances to foods, everyday chemicals and medications, they may be unable to tell which exposures are causing symptoms because triggering exposures occur throughout the day and their symptoms overlap in time.

The use of petroleum-based chemicals has risen dramatically in recent decades. These substances can seriously affect the health of susceptible people. With intense or long-term chemical exposures, these individuals can acquire Toxicant-induced Loss of Tolerance, or TILT. The problem is, currently, it is not always possible to know beforehand who is susceptible—before the parents build a new home or remodel their existing home for a new baby, hire an exterminator to keep bugs away and install air fresheners throughout the house so the home smells nice for baby.

New research suggests the children of chemically intolerant individuals inherit some of their parents’ same susceptibility to developing life-changing chemical, drug and food intolerances if sufficient exposure occurs (e.g., to pesticides, chemicals associated with new construction). The person develops TILT, or as some affected persons refer to the process, they become “TILTed.”

Most but not all chemical exposures are easy to identify by odor. Complex mixtures of chemicals emitted from everyday products used for home construction and furnishings, for example volatile organic chemicals outgassing from new carpet, adhesives, fragrances, etc., can be trapped inside our energy efficient, tightly constructed homes, schools and workplaces. These exposures can be hard to avoid and because of “olfactory adaptation,” our ability to smell complex low-level mixtures is quickly lost—within minutes of entering a home. Think of homes you may have visited while touring builders’ open houses: in your first few breaths you can smell the air, but after several breaths your nose adapts and you are no longer aware. A useful exercise can be to spend several days away from a suspect environment and then return, noting any odors that are apparent within the first breath or two. Or ask neighbors or friends what your house smells like — e.g ., mothballs, new carpet, a fragrance, natural gas or a mixture of substances?

Many of the same environmental exposures that initiate TILT can also interfere with neurodevelopment in a fetus. The harm can start as early as the first month of pregnancy. That’s the stage when the neural tube forms but before most mothers know they are is pregnant.

There are important relationships between autism, genes and exposures. Humans have different thresholds for becoming chemically susceptible. These differences are normal and not defects. These differences are not new. What is new? Our exposures.

Since World War II, the petrochemical era has ushered in countless new chemical exposures. Many of these have found their way into our building interiors where Americans spend on average 90 percent of their day. A mother and infant may spend even more time at home. Not only do indoor exposures vary from house to house and workplace to workplace, but there can be as much as a 10,000-fold difference between individuals in our ability to detoxify and eliminate certain substances from our bodies.

The rise in autism spectrum disorders seems to follow the rise in petrochemical usage, and arouses enough suspicion to justify immediate research.

The need for research is great, and future studies need to focus on potential environmental causes and especially the indoor environment—an area that falls between the cracks in terms of government research funding. There is a saying: “There are no genetic epidemics.” If a condition has become as prevalent as autism, then research must examine potential environmental contributors — and quickly. Although genes play a role in terms of individual susceptibility to exposures, it is the exposures that are the problem, not our genes! In March, Mark Roithmayr, president of the influential organization Autism Speaks, which helped fund the South Korean study, called for a comprehensive national strategy to address the autism epidemic. Among other things, he cited a need to:

• Fund more basic science uncovering the genetic underpinnings of autism.
• Fund more environmental research detecting the causes of autism.
• Accelerate the funding and development of effective medicines and treatments.

I agree with his statement. There are many different types of autism. Autism is an umbrella diagnosis, one that has many potential root causes. However, the “chemical connection” seems be one of the most promising paths toward an understanding of autism spectrum disorder.

Medical researchers are finding that children with autism and their parents suffer in some of the same ways when they encounter certain chemicals in everyday products.

Recently, at the invitation of the Autism Society of America, I presented a national webinar describing how children with autism and their parents often share certain intolerances, and may react in similar ways. Why? I think it’s a case where “Genetics loads the gun, and the environment pulls the trigger.”

We know, for example, that in adults certain acute or chronic chemical exposures sometimes can initiate a process that has come to be known as “Toxicant-induced Loss of Tolerance,” or TILT. TILT may develop after a workplace exposure or remodeling of a home or exposure to petrochemicals or combustion products from a fire. Thereafter, everyday exposures to common chemicals, foods, medications, and even caffeine, can trigger cognitive and mood difficulties, as well as a host of baffling symptoms that can affect the nervous system, digestive tract, airways, and skin.

Notably, many of the same environmental exposures, e.g., certain pesticides, that initiate TILT in adults can also interfere with neurodevelopment in a fetus, starting as early as the first month of pregnancy when the neural tube forms and before the mother even knows she is pregnant!

And, as for chemically intolerant adults, we should make every effort to prevent suspected initiating exposures as well as minimize exposures that can continue to trigger autistic behaviors and other symptoms throughout the lifespan. This also means that continued avoidance of even low-level exposure triggers may be important for treating children and adults with autism.

These differences in susceptibility to environmental chemical exposures, which may predispose to TILT in adults and autism in children, are the consequence of normal human genetic diversity — a good thing! My concern, as we learn more about the important relationships between autism, genes and exposures, is that differences in our genetic susceptibility not be viewed as a defects, but rather normal individual differences. These differences are not new. What is new are our exposures. Since World War II, the petrochemical era has ushered in myriad chemical exposures, exposures unprecedented in human history. There can be as much as a 10,000-fold difference, from person to person, in our ability to detoxify and eliminate substances from our bodies. Currently we are unable predict which exposures can cause TILT or autism in which persons.

Other shared features of autism and chemical intolerance include food cravings (mimicking addiction) and intolerances including gluten (wheat) and milk. From our own studies, mothers of children with autism, compared to mothers of “neurotypical children’” were much more likely to report that common chemical exposures make them sick. These included household cleaners, fragrances and pesticides. We used the validated “Quick Environmental Exposure and Sensitivity Inventory” or QEESI, questionnaire to gauge chemical, food and other environmental intolerances in the mothers. You too can use the QEESI questionnaire to gauge sensitivities.

The underlying causes for autism and the reasons why it now affects a staggering 1 in 110 babies born in the United States — a national epidemic according to the Centers for Disease Control and Prevention (CDC) — continue to elude the medical and scientific communities. There are many clues, and theories. The webinar I presented on behalf of the Autism Society of America, which is available to you free of charge, focuses on the striking and often overlooked parallels between autism and chemical intolerance. The increased use of petrochemically based household products and recent emphasis on greener, more energy efficient homes with little fresh air to dilute contaminants in the United States parallels the rise in autism over the past few decades. Globally, autism has been on the rise in every industrialized nation.

During medical school, my colleagues and I learned that children are not just little adults! There are obvious size and many metabolic differences between children and adults. At the same time, children with autism and chemically intolerant adults are strikingly similar in important ways: They share exposures to petrochemicals, indoor air pollutants and pesticides, and both experience chemical and food intolerances. A crucial difference in the case of autism is timing: Exposures that occur during pregnancy or early childhood have the potential to alter neurodevelopment. One tool that is urgently needed in medicine is an Environmental Medical Unit, or EMU, which would allow physicians and families to determine whether and to what extent autism might be reversible if chemical and food triggers could be avoided systematically for a few weeks. Here is a paper I wrote about EMUs.

Here is the webinar presentation to the Autism Society of America.

To follow the proceedings, you will need to install the Cisco Webex browser software. You will be prompted at the website. Adding the software only takes a few seconds.